Hot dip coating is a well known continuous method for applying a metal coating on metal sheet or tape by passing the tape through a molten bath of the metal. For example, a zinc coating can be formed on a steel sheet or tape by passing the steel tape through a molten bath of zinc.
The molten metal in the bath can react with air, the metal tape, or contaminants on the metal tape to form various oxides or metallic compounds of the molten metal. The oxides and metallic compounds form particles known as dross in the molten metal bath. It is known that some types of dross are buoyant in the molten metal, and float on the surface of the bath. Such floating dross particles can accumulate on the surface of the bath forming large agglomerations that can be deposited on the tape passing through the molten metal bath.
For some applications the coated tape must have a uniform cross section, for example to enable uniform winding of the tape to form coils. Therefore, it is desirable to form a coating having a uniform cross-section with a smooth surface finish in the continuous coating operation. However, the dross particles, and especially the agglomerated dross deposited on the tape can result in a non-uniform cross-section, and an excessively rough surface finish on the coated tape.
One aspect of this invention is a coating apparatus that minimizes the deposition of dross agglomerates on a sheet or tape being coated with molten metal.